Shoe stiffener



Patented Sept. 8, 1931 UNITED STATES: PATENT OFFICE wILLY o. Emmi: AND wonrm warren, or amnion, GERMANY, nssrenons 'ro consoa'rnnu run nnnxrnocnnmscnn mnus'rarn e, m. n. 11., or umen, GERMANY, A coaromrron or GERMANY snon srlrrmma' Ro Drawlng. Application filed lay 31, 1929, Serial No. 367,610, and in Germany June, 1928.

This invention relates to shoe stiffeners.

- made and safely handled b shoe factories. A further-object is to provi e an article that will permanently retain the necessary flexibility and will not contain substances'which are injurious either to the foot or the-leather of which the shoe is made. A-js'till, further objecttis to provide. a material havinggreat power of adhesion so that there is nodanger 1 of the lining or the leather of the shoe separating from the stiffening-material. 2 Heretofore the most satisfactory stiffen! ers has been made by impregnatmg some suitable fabric, generally felt, with a cellu-.

lose ester solution such as celluloid. 'The use of such impregnating material has manydis- 5 advantages, one of the greatest objections being the high cost due to the fact that large volumes of solvent are necessary to incorporate a sufficient quantity of the cellulose ester in the fabric. It is obvious that to give the material sufiicient strength, a considerable quantity of cellulose ester must be absorbed and it has been found impossible to keep high concentrations of ester in solu tion or to keep the viscosity sufficiently low 5 to handle the im regnationfrom a practical point of View. s a result, several impregnations are necessary. Moreover, 'the stiffening material upon drying is too brittle and has a strong tendency to crack when theshoe 40 is subjected tothe ordinary strain encountered in wear. This latter objection has been overcome by the addition of plasticisers to the impregnating solution, the eflect of which is to give the stiffening material a satisfactory initial flexibility, but this effect is not permanent, due to the fact that the plasticiser slowly volatili'zes and leaves the material brittle. An added objection to this plasticiser is that it has an in'uriou's' ef- 6 0 feet on both the shoe leather an the foot.

It is apparent, therefore, that the addition of plasticisers is far from satisfactory.

' A further disadvantage in'the shoe stiffeners heretofore commonly used lies in the fact thatthe impregnating materials possess very inferior adhesive properties, giving no assurance that the stiffening material'will permanently adhere to either the lining or the overlying leather of the shoe, and furthermore, a solvent of the cellulose ester must .beibrought in contact with the material to develop even this inferior adhesive Property the imregnated fabric while theimpregnating s0- utiou is still wet, obviously an impractical procedure in a shoe factory, or the steaming of stifiener in some cellulose ester solvent just before use. As the solvent vapors suitat all, This necessitates the use 0 able for the cellulose esters are extremely inflammablejthis latter procedure is a source l of constant danger and must necessarily be done in the immediate vicinity ofthe shoe factor in order .to use the stiffener before .the'ce lulose ester sets again.

. We have found that by impregnating the stiffening material with a solution of poly vinyl acetate all of these disadvantages are overcome. The alcohol and benzene soluble modifications of poly vinyl acetate are particularly adapted for this use and have the added advantage of being readily soluble in relatively cheap solvents, alcohol and-benzene. In contrast to the cellulose estertolutions, alcohol solutions of poly vinyl acetate can easily be made having a -70% poly vinyl acetate content and having relatively greater fluidity than the cellulose ester solutions of far lower solid content. A single impregnation of such a poly vinyl acetate solution gives the stifi'ener sufiicient strength,

whereas the cellulose, ester solution has such a low solid content-that several impregna- .t1ons are-necessary and as a result consider.-

able quantities of valuable solvents are lost.

procedure the fire hazard is totally eliminat ed in the shoe factory as the stifiener im- 1 pregnated with poly ving'l acetate isnon-t inflammable and none 0 the inflammable solvents need ever enter the factory.

The poly vinyl acetate has a property of remaining permanently flexible to some extent so that the addition of plasticisers is unnecessary, thereby doing away with the offensive odors of these materials as well as their deleterious effect on the foot and shoe leather. It will be understood that such plasticisers can be added to our poly vinyl acetate solution if found desirable, but as a eneral 2. A shoe stifi'ener comprising a sheet of felt cloth impregnated with alcoholand benzene-soluble poly vin l acetate.

Signed at day of May,

rule, the disadvantage of these ad itionalcompounds outwei h the advantages in as much as the poly vinyl acetate is sufliciently flexible alone.

Example I A felt webbing is impregnated by immersion in a solution of poly vinyl acetate in alcohol and dried. The dry material possesses exceptional strength and is sufliciently flexible for use in either the box toe or the heel counter of a shoe. It is only necessary to warm this materialto form it into the desired shape and upon cooling it will regain its original strength. The stillening material thus shaped can be united with the lining and the leather of the shoe by warming to approximately C. or, if it is desired, the adhesive property can be I developed by exposing the material to a poly vinyl acetate solvent.

Besides the solution of poly vinyl acetate be used in like manner: acetone, benzene, butyl acetate, toluene, .zene, methyl alcohol, acetals.

Example 22 acetic ether, chlorobenparts by weight of polyviny 'c acetate-in 55 1= partsof ethylacetate. A sheet 'of cloth is 11l1prel11at8d by immersion with this solution, 'ed'andrusedfor shoe-stiffening pur- The invention "claimd is: r 1. A shoe stiffener comprising a sheet of V cloth impregnated with alcoholand benzenesoluble poly vinyl acetate.

in alcohol, the following solutions can also A solution is prepared b dissolving 45 Munich, A. D1929.

WILLY O. HERRMANN. WOLFRAM HAEHNEL.

ermany, this 16th 

